Delivery of certain wavelengths of radiant energy is facilitated by transmission along flexible silica fibers. The energy is dispersed from the emitting end of an optical fiber in a widening cone. The energy intensity is generally symmetric about the central fiber axis (i.e., uniformly distributed in azimuth) at the emitting end. The distribution of emitted energy orthogonal to the azimuth angle is highly non-uniform, with highest intensity at the central axis, rapidly decreasing with increasing divergence angle relative to the central fiber axis, sometimes approximated by a power cosine function of the divergence angle.
Energy beam guiding structures are known that use refractive media (e.g. optical lenses) in combination with movable reflective media (e.g. mirrors) to focus and direct diverging radiant energy disposed around the input beam axis to a target of interest. The optical lenses typically convert (collimate) the dispersing radiant energy to a second beam with the radiant energy directed more parallel to the input beam axis. The second beam's energy is distributed over a cross-sectional area defined on a target surface oriented in a transverse plane intersecting the optical axis of the second beam. The size of the defined area is typically limited by the diameter of the lenses. The movable reflective media are coupled to transporting mechanisms and are positioned to modify the direction of the collimated beam as a function of time, typically in a raster pattern scan mode. The dynamic positioning of the reflective media is generally arranged so that the second beams energy, averaged over a multiple number of scan cycles, is distributed as a less intense, more uniform energy intensity distribution over the desired target surface area.
The raster scan mode can be described as periodic deflection of the input beam away from its input axis, in which the period is composed of alternate, orthogonal scanning and stepping cycles. Typically during the scanning cycle the beam is deflected along a first transverse orthogonal axis (e.g. x-direction) at a first angular or linear rate that is constant over each scanning cycle. Next the beam is stepped by a second fixed angular or linear increment, in the direction (e.g. y-direction) orthogonal to both the input beam axis and the first scan axis.
The x-scan rate, scan width, y-step angle (increment) and period are selected to distribute the high intensity energy of the input beam over a larger surface area than that provided directly by the lenses. In addition, one or more condensing (focusing) lens is typically used to focus the collimated beam energy to a fine point at the target's surface. Combinations of mirrors and lenses are used to achieve both effects. The typical objective of these combined reflective and refractive elements is to modify the beams intensity distribution over the width of a limited transverse area and to move the scan area over a target surface to produce a less intense, more uniform, energy intensity distribution over a larger area.
In previous laser scanning heads, the beam is typically reflected from two raster scanning mirrors movably mounted in a housing where they are disposed with the first mirror intercepting the input beam, reflecting it to the second, which then reflects the beam toward the target.
Typically the second mirror is spaced away from the first at a right angle from the input beam axis (i.e. where the beam is reflected nearly 90 degrees away from and back along the housing axis). This type of reflective system results in unavoidable reflective energy loss at each reflection. Such systems may have a housing that is somewhat bulky in section transverse to the direction of the scanning beam to allow for the spacing between first and second mirror surfaces.
Condensing and focusing lenses are sometimes used in conjunction with scanning heads. For example, U.S. Pat. No. 5,780,806 by Ferguson et al., (columns 7 and 8) discloses a reflective scanning laser ablation system in which lenses are used as refractive elements for collimating and focusing a scanning output laser beam.
U.S. Pat. No. 5,204,523 by Appel et al., discloses in claim 1 a method for slowly scanning a beam by refraction of light by an amount determined by varying the wavelength of the light beam. The amount and rate of scanning are relatively small and not conducive to high power laser beam scanning, however.
U.S. Pat. No. RE 33,777 by Woodroffe, Dec. 24, 1991 discloses Laser removal of poor thermally conductive materials, but does not elaborate on beam delivery methods.
U.S. Pat. No. 5,643,476 by Garmire, et al., Jul. 1, 1997 shows a Laser system for removal of graffiti. The beam steering mechanism disclosed uses reflective media with the consequent reflective energy loss.